During refueling in which fuel (fuel oil) is charged into an automotive fuel tank, fuel vapor is generated. PATENT DOCUMENT 1 describes handling of fuel vapor generated during such refueling, in which an upper end portion of a fuel filler pipe is connected through a breather pipe to a fuel tank, the fuel vapor is released from the fuel tank through the breather pipe toward a fuel filler gun (the upper end portion of the fuel filler pipe), and is returned to the fuel tank. However, in such a system, fuel vapor tends to leak through a fuel filler pipe to the outside during refueling. To address this problem, PATENT DOCUMENT 2 describes that a canister configured to absorb evaporated fuel is connected to a fuel tank through a fuel vapor pipe (evaporator pipe), and fuel vapor generated in the fuel tank during refueling is discharged to the canister.
The fuel vapor absorbed by the canister is purged (released) through a purge pipe to an intake system of an engine. An automobile having such a fuel vapor purging system preferably includes a diagnostic system for finding leakage of fuel vapor due to, e.g., perforation in order to ensure the reliability of the system. For example, PATENT DOCUMENT 3 describes that a pressure sensor for a fuel vapor path including a fuel tank, a fuel vapor pipe, and a canister is provided to detect leakage of fuel vapor based on a change in the pressure of the fuel vapor path.